Electron Microscopy Characterization of Bursera cuneata Schltdl Residues for its Application as Solid Biofuel

Biomass is a resource that has energy potential to meet the demand of society [1]. Specifically, lignocellulosic biomass is a promising source of renewable energy, which can be converted into thermal energy in the form of solid type biofuels [2], which can be a non-polluting and locally available generation alternative, which it can promote the satisfaction of regional needs from a global perspective [3]. In this sense, the present investigation shows an alternative for the energy use of the timber residue Bursera cuneata Schltdl (copalillo), a timber forest resource, which is generated in artisan workshops for the manufacture of ornamental products, with the intention of identifying the available energy potential and its possible application to meet local energy needs in indigenous communities in Mexico. Bursera cuneata Schltdl residues were collected in artisan workshops for ornamental wood products located in the indigenous community of Tocuaro, Michoacán, Mexico (19.539953, -101.693959). To estimate the volume of waste generated, a quantitative and qualitative evaluation instrument was applied, through open interviews and the use of digital hook scales. The morphology of the collected residues was analyzed using scanning electron microscopy (SEM) images, using a Hitachi SU 3500 microscope equipment, with an acceleration voltage of 20 kV; a semi-quantitative chemical analysis was also performed by energy dispersive x-ray spectroscopy (EDS). The calorific value was also estimated using a Leco AC 500 bomb calorimeter based on the ASTM D2015 standard [4]. Figure 1 (a), (b), and (c) shows the waste generation process from the cutting of the forest resource, the processing to manufacture handicrafts, and the accumulation of waste in each workshop of the study community. The residues of Bursera cuneata Schltdl turn out to be quite porous as shown in Figure 1(d) and (e), showing micrometric cavities. The spacing seen in the morphology of these residues also provides a lower density compared to species such as Quercus spp. and the Pinus spp that are located in the analysis region. The results of the semiquantitative chemical analysis allowed us to identify that more than 95% of the weight of the material is attributed to compounds formed by Carbon and Oxygen that, being an organic material with forest characteristics, correspond to polymeric compounds such as cellulose, hemicellulose, and lignin, compounds that they contribute to the energy content of the material [2]. The resulting calorific value was 19.1 MJ/kg, a high value compared to the forest resources that are used in combustion to meet local energy needs [2]. The generation of Bursera cuneata Schltdl waste per workshop is estimated at approximately 300 kg per month, which represents an energy potential of the order of 68.7 GJ/year, and a technical potential with uninsulated wood stoves (Efficiency = 10%) of 6.8 GJ/year per workshop. This resource can be used for the manufacture of solid biofuels, increasing its calorific value by unifying the material, and due to its local availability, it represents a renewable, fair, and affordable energy source. The characterization carried out using SEM allowed us to know the morphology of the Bursera cuneata Schltdl residues and to infer the presence of polymeric compounds that are usually present in this type of forest resources, which contribute to the calorific value of the material. Therefore, these residues have the potential for bioenergy use to meet the local energy demand sustainably. Waste generation process of Bursera cuneata Schltdl: (a) cutting (b) manufacture of handicrafts (c) accumulation of waste. SEM: (d), (e) morphology (f) (g) semiquantitative chemical analysis (SEM-EDS).